${{\mathit n}}$ $\rightarrow$ ${{\mathit p}}{{\mathit e}^{-}}{{\overline{\mathit \nu}}_{{{e}}}}$ DECAY PARAMETERS

See the above “Note on Baryon Decay Parameters.” For discussions of recent results, see the references cited at the beginning of the section on the neutron mean life. For discussions of the values of the weak coupling constants ${\mathit g}_{{{\mathit A}}}$ and ${\mathit g}_{{{\mathit V}}}$ obtained using the neutron lifetime and asymmetry parameter$~\mathit A$, comparisons with other methods of obtaining these constants, and implications for particle physics and for astrophysics, see DUBBERS 1991 and WOOLCOCK 1991. For tests of the $\mathit V−\mathit A$ theory of neutron decay, see EROZOLIMSKII 1991B, MOSTOVOI 1996, NICO 2005, SEVERIJNS 2006, and ABELE 2008.

${{\mathit e}^{-}}$ ASYMMETRY PARAMETER $\mathit A$

INSPIRE   PDGID:
S017BA
This is the neutron-spin electron-momentum correlation coefficient. Unless otherwise noted, the values are corrected for radiative effects and weak magnetism. In the Standard Model, $\mathit A$ is related to $\lambda {}\equiv\mathit g_{A}/\mathit g_{V}$ by $\mathit A$ = $-2$ $\lambda $ ($\lambda $ + 1) $/$ (1 + 3$\lambda {}^{2}$); this assumes that $\mathit g_{A}$ and $\mathit g_{V}$ are real.
VALUE DOCUMENT ID TECN  COMMENT
$\bf{ -0.11958 \pm0.00021}$ OUR AVERAGE  Error includes scale factor of 1.2.  See the ideogram below.
$-0.11985$ $\pm0.00017$ $\pm0.00012$ 1
MAERKISCH
2019
SPEC pulsed cold ${{\mathit n}}$, polarized
$-0.12015$ $\pm0.00034$ $\pm0.00063$ 2
BROWN
2018
UCNA Ultracold ${{\mathit n}}$, polarized
$-0.11926$ $\pm0.00031$ ${}^{+0.00036}_{-0.00042}$ 3
MUND
2013
SPEC Cold ${{\mathit n}}$, polarized
$-0.1160$ $\pm0.0009$ $\pm0.0012$
LIAUD
1997
TPC Cold ${{\mathit n}}$, polarized
$-0.1135$ $\pm0.0014$ 4
YEROZOLIMSKY
1997
CNTR Cold ${{\mathit n}}$, polarized
$-0.1146$ $\pm0.0019$
BOPP
1986
SPEC Cold ${{\mathit n}}$, polarized
• • We do not use the following data for averages, fits, limits, etc. • •
$-0.11972$ $\pm0.00025$ 5
SAUL
2020
SPEC Cold ${{\mathit n}}$, polarized
$-0.11952$ $\pm0.00110$ 6
MENDENHALL
2013
UCNA See BROWN 2018
$-0.11966$ $\pm0.00089$ ${}^{+0.00123}_{-0.00140}$ 7
PLASTER
2012
UCNA See MENDENHALL 2013
$-0.11966$ $\pm0.00089$ ${}^{+0.00123}_{-0.00140}$
LIU
2010
UCNA See PLASTER 2012
$-0.1138$ $\pm0.0046$ $\pm0.0021$
PATTIE
2009
SPEC Ultracold ${{\mathit n}}$, polarized
$-0.1189$ $\pm0.0007$ 8
ABELE
2002
SPEC See MUND 2013
$-0.1168$ $\pm0.0017$ 9
MOSTOVOI
2001
CNTR Inferred
$-0.1189$ $\pm0.0012$
ABELE
1997D
SPEC Cold ${{\mathit n}}$, polarized
$-0.1160$ $\pm0.0009$ $\pm0.0011$
SCHRECKENBACH
1995
TPC See LIAUD 1997
$-0.1116$ $\pm0.0014$
EROZOLIMSKII
1991
CNTR See YEROZOLIMSKY 1997
$-0.114$ $\pm0.005$ 10
EROZOLIMSKII
1979
CNTR Cold ${{\mathit n}}$, polarized
$-0.113$ $\pm0.006$ 10
KROHN
1975
CNTR Cold ${{\mathit n}}$, polarized
1  MAERKISCH 2019 further derive a value for the CKM-element $\vert {{\mathit V}_{{{ud}}}}\vert $ = $0.97351$ $\pm0.00060$, using ${\mathit \tau}_{{{\mathit n}}}$ = 879.7(8) sec and the relation from CZARNECKI 2018.
2  BROWN 2018 gets $\mathit A$ = $-0.12054$ $\pm0.00044$ $\pm0.00068$ and $\lambda $ = $-1.2783$ $\pm0.0022$. We quote the combined values that include the earlier UCNA measurements (MENDENHALL 2013).
3  This MUND 2013 value includes earlier PERKEO II measurements (ABELE 2002 and ABELE 1997D), with a correction to those results.
4  YEROZOLIMSKY 1997 makes a correction to the EROZOLIMSKII 1991 value.
5  Under the SM assumption that the Fierz term ${{\mathit b}}$ = 0, SAUL 2020 obtain the quoted asymmetry parameter ${{\mathit A}}$ and $\lambda $ = $-1.27607$ $\pm0.00068$. In a combined fit authors extract the values ${{\mathit A}}$ = $-0.1209$ $\pm0.0015$, $\lambda $ = $-1.2792$ $\pm0.0060$, and ${{\mathit b}}$ = $0.017$ $\pm0.021$.
6  MENDENHALL 2013 gets $\mathit A$ = $-0.11954$ $\pm0.00055$ $\pm0.00098$ and $\lambda $ = $-1.2756$ $\pm0.0030$. We quote the nearly identical values that include the earlier UCNA measurement (PLASTER 2012), with a correction to that result.
7  This PLASTER 2012 value is identical with that given in LIU 2010, but the experiment is now described in detail.
8  This is the combined result of ABELE 2002 and ABELE 1997D.
9  MOSTOVOI 2001 calculates this from its measurement of $\lambda =\mathit g_{\mathit A}/\mathit g_{\mathit V}$ above.
10  These results are not corrected for radiative effects and weak magnetism, but the corrections are small compared to the errors.

           ${{\mathit e}^{-}}$ asymmetry parameter $\mathit A$
References